The present invention relates to a three-dimensional image display device for displaying the spatial distribution of the physical matter of a specimen in the form of a three-dimensional image.
Since the advent of the potential for producing precision tomogram data showing the physical matter of a body using x-ray CT devices, it has become possible to render three-dimensional images using multiple sets of tomogram data captured from different cross-section positions. In particular, it has become possible to reconstitute three-dimensional images with even greater precision due to the recent use of helical scan x-ray CT devices and multi-beam x-ray CT devices.
In order to construct a precise three-dimensional image, it is desirable to make the cross-section images and cross-section image spacing as narrow as possible in terms of the cross-sections that are used in constructing the three-dimensional image. With recently implemented multi-beam x-ray CT devices, x-ray detectors are divided along the body axis of the specimen perpendicular to the cross-sections, and by this means, more narrow cross-section image spacing (slice gap) and thinner cross-section images (slice width) have been achieved relative to conventional x-ray CT devices.
When using image data having narrow cross section gaps and cross section thicknesses captured using multi-beam x-ray CT devices, it is possible to produce three-dimensional images that are more detailed than those obtained using image data captured with a conventional x-ray CT device. For this reason, the range of diagnostic use of three-dimensional images produced using x-ray CT image data is greatly increased, and the technology is being used towards a wider variety of ends.
With multi-beam x-ray CT devices, it is possible to capture image data with thin cross-sections and narrow cross-section image gaps more rapidly than with conventional x-ray CT devices. However, the clinical requirement in terms of length along the axis of a body is the same as in the past, so the number of image data slices or image data volume is greatly increased.
With conventional x-ray CT devices, the number of image data slices captured in a single investigation is in the range of a few tens of slices. In general, the image is imaged on film using a multiformat camera, and this film is then generally used for observation or reading. However, with multi-beam x-ray CT devices, hundreds of cross-sectional images taken in a single investigation are used in the reproduction of an image, and so imaging these on film with a multiformat camera, and selecting them and observing or reading them is problematic. In light of these considerations, the necessity of constructing a three-dimensional image, and then observing or reading this image is additionally increased.
Thus, multi-beam x-ray CT devices are revolutionary in that they allow the collection of image data having a thin cross-section and cross-section image gap in a shorter period of time than with conventional x-ray CT devices. However, because the number of slices of reconstructed images that are obtained is greatly increased, the load on a network that is transmitting this data is greatly increased, leading to the necessity of high-speed networks. Moreover, picture archival and communication systems (PACS) must also have increased capacity and speed in order to deal with the increase in data. Linked three-dimensional image display devices can receive large quantities of data in a short period of time, and so the necessity has developed for a high-performance system that performs image processing on large quantities of data in a short period of time.
In terms of three-dimensional display methods used with medical images, there are surface rendering techniques whereby the shape of the domain surface is displayed after extracting the domain surface of the object that constitutes the specimen, and volume rendering techniques that treat the specimen as a three-dimensional array of voxels having values corresponding to physical properties.
The surface rendering method creates a three-dimensional image of the object to be displayed by means of the following processes carried out on each of numerous x-ray CT images. 1) extraction of a domain containing an object by threshold value processing that designates an upper and lower limit for CT values held by an object, 2) extraction of the domain of a display object by means of eliminating domains not related to the display object from this domain, 3) extraction of the contour of this domain, 4) production of a solid using the respective contours obtained from multiple slices of the x-ray CT image, and 5) final shadowing and projection processing on the solid, thereby displaying the object to be displayed as a three-dimensional image.
Volume rendering techniques handle voxels possessing opacity and color data corresponding to the physical properties of a specimen as a three-dimensional array, and by carrying out shadowing and projection processing, referred to as ray casting, on this array, the physical properties of a specimen are displayed as a three-dimensional image. Because each voxel possesses color and opacity levels corresponding to the CT values thereof, it is possible to display domains having different CT values as different colors and opacities.
With volume rendering techniques, 1) a three-dimensional voxel array is constructed using x-ray CT image data from multiple slices, 2) the color and opacity are set for a range of CT values possessed by the object of interest, and 3) shadowing and imaging processing known as ray casting are carried out, thereby displaying the object of interest as a three-dimensional image. By setting different colors and opacities for different CT value ranges, it is possible to display domains having different CT values as different colors and opacities.
Although it is necessary to carry out domain extraction for each of the multiple x-ray CT image slices when using the surface rendering technique, a domain extraction operation is not necessary with the volume rendering technique. With the human body, there are many cases where CT values vary continuously in a boundary domain having two anatomical structures, and so the effect of eliminating the domain extraction work is significant. In addition, in comparison to surface rendering techniques, a more natural and smooth shading can be obtained for edges having boundaries that change abruptly.
With volume rendering techniques, three-dimensional voxel arrays constructed using x-ray CT image data are classified based on the object, and the anatomical structural elements of the specimen are classified based on CT values. Consequently, spatial domains having different CT values can be handled as different objects, but spatial domains having the same CT value, for example, are handled as a single object, even with objects that are in physically distinct locations. This is inconvenient for cases in which spatial domains having the same CT values are to be handled as two or more objects.
Thus, with volume rendering techniques, spatial domains having different CT values can be handled as different objects, but spatial domains having the same CT values are handled as a single object, even when the spatial domains having the same CT values are in physically distinct locations. Consequently, as with operation simulations, for example, when a spatial domain having the same physical properties is to be separated and handled as two or more objects, it is necessary to carry out image processing or manipulations in order to separate spatial domains.
FIG. 1 is a block diagram showing a conventional three-dimensional image display device and its network environment. The x-ray CT device 101 collects x-ray CT data from multiple cross-sections of a specimen, reconstructs them, and produces image data for the multiple cross-sections. The PACS server 102 is an image storage and supply system whereby data is collected and reconstructed image data is stored for multiple modalities including the x-ray CT device 101, and whereby data is transported to users as necessary. The three-dimensional image display workstations 121, 122, 123, . . . are three-dimensional image display workstations that retrieve image data collected and stored by the x-ray CT device 101 or PACS server 102 via a network 111, and then use this image data in order to construct three-dimensional images. The network 111 is a high-capacity, high-speed network whereby large quantities of image data are transmitted to three-dimensional image display devices from an x-ray CT device 101 or PACS server 102. The user that constructs the three-dimensional image employs a three-dimensional image display workstation 121, 122 or 123, where image data is obtained from the x-ray CT device 101 or PACS server 102 via the network 111, and this data is then used in constructing the three-dimensional image.
FIG. 2 is a block diagram showing an example of a conventional workstation structure. The central processor 301, memory 302, display processing circuitry 303, display device 304, computer bus 305, data storage device 306, network interface 307 and control device 308 that constitute the workstations all have the same functions as with common personal computers, but a system in which the performance of these constitutive elements is enhanced is commonly used. The high-speed computing device 309, high-capacity memory 310 and high-speed computater bus 311 are commonly used in work-stations in order to process large amounts of information at high speed. The workstations have high image processing capacity relative to common personal computers, and in general are higher in cost.
FIG. 3 is a block diagram showing the function of a conventional three-dimensional image display device. The three-dimensional image display workstation 121 acquires image data via a high speed network 111 from an x-ray CT device 101 or PACS server 102. The data storage device 201 is a magnetic disk device or other such device, which stores the acquired data. The image data selected by the data indicator panel 228 through operation of the control device 211 is designated by a data designation signal 229 read from the data storage device 201, and transferred to the preprocessor 202. After correction of the slice gap and correction of the frame inclination angle performed at the preprocessor 202, the data is stored as voxel data in a three-dimensional voxel storage device 203.
The object setting part 221 is a subsystem for setting the parameters to be used in constructing a three-dimensional image from both the space domain and CT value ranges. Numerous subsystems 221-1, 221-2, 221-3, . . . are provided for establishing multiple objects. The object space domain setting subsystems 222-1, 222-2 . . . , set the parameters of the various object space domains. The object parameter setting subsystems 223-1, 223-2, . . . set the opacity and color as functions of the object CT values. The object parameters 224-1, 224-2, . . . are stored as these set values.
Image processing is carried out using object parameters 225 established by the subsystem 221 for the voxel data of the three-dimensional voxel storage device 203, and the processing results are stored in three-dimensional voxel 204. The three-dimensional voxel 204 retain density, gradient and color values in the space location corresponding to the voxel data in the three-dimensional voxel storage device 203.
The ray casting operation part 205 involves ray casting using projection parameters 227 established by the subsystem 226 which sets the projection processing for voxel data that is stored in the three-dimensional voxel 204 having density, gradient and color values. By this means, the volume-rendered image data is constructed.
The volume-rendered image data produced by the ray casting process at the ray casting operation part 205 is subjected to post-processing involving affine transformation (data compression) at a post-processor 206. Subsequently, the image is displayed on the CRT display or liquid crystal display of the image display device 207.
The control device 211 is used for data designation, object parameter setting, and projection process parameter setting, and is operated by a keyboard or mouse.
Because it is necessary to transport a large quantity of data from the x-ray CT 101 or PACS server 102 in FIG. 3 to the three-dimensional image display workstations 121, traffic on the network 111 is high. Because it is necessary for the transport time to be short in order that the users can function efficiently, a high-speed, high-capacity network is generally used for the network 111. In addition, because the data storage device 201, and the preprocessor 202, three-dimensional voxel storage device 203, three-dimensional voxel 204, ray casting operation part 205 and post-processor 206 in the three-dimensional image display workstation 121 are parts that carry out image processing using large amounts of data, it is necessary for them to have rapid responses in order to prevent stress on the part of the user. Consequently, high-speed image processing is required in these parts, and a high-speed workstation is commonly used to this end for the three-dimensional image display device.
Because it is easy to grasp the solid structure of a specimen more readily from a three-dimensional image than from a two-dimensional image, three-dimensional image display devices are widely used. However, skill is necessary in operating the device so that a diagnostically useful, three-dimensional image is obtained via surface rendering techniques as well as the volume rendering techniques. In addition, because a large quantity of data is used in order to produce a three-dimensional image, a high-speed network is required in order to rapidly transport large quantities of data, and a high-capacity, high-speed data processor is required that can process large quantities of data in a short period of time. Consequently, it is often the case that a specialist will produce three-dimensional images. However, when reporting to the requesting department, he/she only sends a printed copy or simply a written diagnosis. Currently, there are few situations where a three-dimensional imaging device is used at the requesting department in order to produce a three-dimensional image for diagnostic use.
The present invention was developed in order to solve the above problems, and to this end, offers a three-dimensional image display device in a network environment wherein a three-dimensional image processing server is situated in the vicinity of an x-ray CT device or PACS server network, imaging is carried out whereby a three-dimensional image is produced from the x-ray CT image data by the three-dimensional image processing server, parameters required for producing a three-dimensional image at the three-dimensional image processing server are designated in the respective personal computers that are linked to the network, and the three-dimensional images constructed at the three-dimensional image processing server are displayed on the respective personal computers. The central three-dimensional image processing server performs processing of large amounts of x-ray CT image data in order to construct a three-dimensional image, and each of the personal computers that is linked to the network may be used to designate parameters required for constructing the three-dimensional image by the three-dimensional image processing server, and to display the three-dimensional images produced by the three-dimensional image processing server.
The user that performs three-dimensional image processing of the x-ray CT image data first designates x-ray CT data to be used in constructing the three-dimensional image using the personal computer, and designates parameters such as object space domains and CT value ranges, and projection processing parameters for three-dimensional image display. When this occurs, the image processing server will construct a three-dimensional image, and the results will be sent to the personal computer, which will then display the resulting image.
A single user thus can share a three-dimensional image process with a number of users by designating x-ray CT data to be used in constructing the three-dimensional image from a single personal computer, designating parameters such as object space domains and CT value ranges, and designating projection processing parameters for three-dimensional image display, allowing production of a three-dimensional image by the three-dimensional image processing server, and transmitting the results to multiple personal computers, which then each display the resulting image. For example, it is possible for radiology specialists and the referring physician in the requesting department to simultaneously observe the three-dimensional image that is being constructed. This improves understanding on the part of the referring physician by facilitating mutual understanding between the referring physician and the radiographic specialist. This stands in contrast to cases where the three-dimensional image constructed by a radiographic specialist is sent via film, etc., to the referring physician of the requesting department.
In the past, users performing three-dimensional image processing using x-ray CT image data have employed workstations for three-dimensional image processing connected to an x-ray CT device or PACS server. In this system, the x-ray CT data that is used in order to construct the three-dimensional image is transmitted from the x-ray CT device or PACS server to the three-dimensional image processing workstation, and the three-dimensional image is constructed at this workstation based on the designation of object space domains or CT value range parameters and designation of projection processing parameters for three-dimensional image display, followed by display of the resulting image. For this reason, it is necessary to install costly three-dimensional image processing workstations at each site where a worker is to perform three-dimensional image processing. In addition, it is necessary to lay out a high-speed high-capacity network between locations where each of the users is to perform three-dimensional image processing so that a large volume of x-ray CT data used in order to construct the three-dimensional image can be transferred from the x-ray CT device or PACS server to the workstations for three-dimensional image processing. Network traffic is also increased.
The term xe2x80x9cobjectxe2x80x9d used herein is an anatomically-related domain, and is a collection of image elements having CT values in the designated CT value ranges located in the designated space domain.
The term xe2x80x9cobject parametersxe2x80x9d used herein are parameters that define the object, designate the space domain in which the image elements that constitute the object are present, and designate the CT value ranges possessed by the image elements that constitute the object. Opacity and color corresponding to the set CT values are designated in the image elements that constitute the object. Three-dimensional data is constructed by using object parameters to operate on the three-dimensional voxel image element values.
The term xe2x80x9cprojection processing parametersxe2x80x9d refers to the parameters used when an image of a three-dimensional object is constructed by projection.